Rangers are deriving immense satisfaction from delaying a Celtic party. Lee McCulloch's last-minute goal at Motherwell denied Celtic the opportunity to formally clinch the Scottish Premier League title when St Johnstone visit Glasgow's east end on Sunday. McCulloch's intervention, then, would prove as much of a sickener to Neil Lennon and Celtic as to Motherwell. And they had plenty of cause for upset; Rangers' winning goal arrived in the most scrappy of circumstances.

It was probably of secondary importance to the Rangers support that their team have now moved six points clear of Motherwell in the chase for second place in the league. It is a decade and now 37 matches since Motherwell defeated Rangers.

Given the intensity of the Old Firm, Rangers will utterly relish the annoyance they caused Celtic for a second week in succession, despite the inevitability of Lennon's men reclaiming the SPL trophy at some point. Now, the odds are stacked in favour of Celtic having the chance to be crowned at Kilmarnock's Rugby Park, where they go next Saturday, for a third time in eight years. Rangers won the league at the same venue last season.

Ally McCoist denied Celtic's potential celebrations featured at all in his thoughts. The Rangers manager did, though, play down reports of a £2m bid from West Brom for Steven Naismith. "Not to my knowledge," McCoist said. "The administrators have been very good at keeping me up to speed with everything so I would be very surprised if there was a bid and I don't know about it."

The match referee here, Iain Brines, was the fourth official in last weekend's Old Firm match and his allegations were central to the dismissal of Lennon from the dug-out. If that affair was simply contentious, the first-half showing of Brines at Fir Park was simply bad. Far too frequently, this referee attracts attention for the wrong reasons.

Brines blundered in not handing Rangers a 29th-minute penalty, instead booking Sone Aluko for diving when his shin was clearly caught by the advancing home goalkeeper Darren Randolph. Even if he did not deem the affair worthy of a spot-kick, it was nonsensical to show Aluko a yellow card. To add to Rangers' ire – and although he will say otherwise – the referee actually seemed to signal for a penalty initially. In the lead up to that foul, Brines also failed to spot a handball by Motherwell's Tim Clancy.

By that stage, the teams had already traded goals. The pacey Chris Humphrey was the architect of the Motherwell opener, with a bursting run that enabled him to elude the visiting defence. With Allan McGregor drawn, Humphrey laid the ball back perfectly for Henrik Ojamaa, who duly stroked home.

Rangers drew level three minutes later. Steven Whittaker scored his first goal of the season with a fine, swerving effort from 25 yards. Randolph, deceived by the flight of the ball, was motionless.

Controversy arrived between the equaliser and that Aluko incident. Clancy can consider himself fortunate to escape with a yellow card, having butted Whittaker's chest. The failure of Whittaker to make much of the illegal challenge looked as pertinent as Brines's failure to apply the laws correctly.

Following the goals, Motherwell were denied when afforded the best chance of the opening period as McGregor saved smartly with his feet from Nicky Law.

Lasley and Steven Davis traded goal attempts in the second half's early stages. With Aluko prominent, Rangers enjoyed territorial possession without forcing Randolph into meaningful action.

The opposite was true of McGregor. The Scotland goalkeeper produced a stunning save to keep out Michael Higdon's side-footed attempt. McGregor's intervention was to prove crucial.

As Randolph offered a reflex stop to deny Aluko, it looked like typifying Rangers' frustrating day. McCulloch had time to prove otherwise.

Motherwell had hitherto defended admirably but were deceived by a Ross Perry throw-in, which was allowed to bounce twice inside the penalty area before landing at McCulloch's feet. The former Motherwell striker bundled home as Clancy claimed for a push in his back; Rangers' delight was clear, but a penny for the thoughts of Lennon.